1. Field of the Invention
The present invention relates to an air damper for generating a negative pressure in a head chip which is applicable to, for example, a printer or a facsimile, and to an ink jet head and an ink jet recording apparatus.
2. Description of the Related Art
Up to now, an ink jet recording apparatus has been known in which an ink jet head for discharging ink from plural nozzles is employed to record characters and/or images on a recording medium. In this type of ink jet recording apparatus, an entirety of the desired area is printed by repeating the following operations. That is, a carriage mounted with the ink jet head is moved in a main scanning direction with respect to the recording medium while the ink is discharged from a nozzle of the ink jet head, thereby printing a dot pattern in a predetermined area; and after one main scanning operation ends, the recording medium is moved in a sub-scanning direction by a predetermined amount.
In a large ink jet recording apparatus, plural ink jet heads corresponding to respective ink colors are mounted to the carriage. This type of large ink jet recording apparatus in which the heads are mounted to the carriage and the carriage moves in the main scanning direction is called a “shuttle type recording apparatus”. The so-called shuttle type recording apparatus is structured such that, in order to perform a large amount of printing for a long period of time, an exchangeable large-capacity ink cartridge is incorporated in the apparatus and connected to the corresponding head through a tube to supply ink. In a method of supplying ink using a tube, when a carriage moves, the ink residing inside the tube moves therein in accordance with the movement of the carriage. When the ink moves, inertia is generated inside the head connected to the tube. Then, a differential pressure due to the inertia inside the head results in breakage of a meniscus that is formed by surface tension of the ink in a nozzle hole provided in a nozzle surface of the head. Thus, the ink cannot be discharged. In view of the above, a part called an “air damper” is generally mounted so as to relax the pressure fluctuation due to the inertia of the ink. In order to relax the pressure fluctuation, one side of the air damper is molded from a rigid body such as plastic to have a recessed portion for storing ink, and a film-shaped sheet is then bonded thereto by thermal welding or the like so as to seal the recessed portion. The film moves due to the pressure fluctuation of the ink in accordance with the movement of the carriage, thereby relaxing the pressure fluctuation of the ink.
If the large ink jet recording apparatus is employed, it is necessary to increase a length of the tube for supplying the ink from the ink cartridge. The longer tube increases a flow path resistance inside the tube to disturb flow of the ink. Also, if an outside air temperature becomes low, viscosity of the ink increases to harden the ink. Thus, smooth flow of the ink is hindered under only an ordinary suction pressure. There can be employed another method of supplying ink by providing a sub-tank in the vicinity of a head. However, a larger apparatus becomes necessary, which leads to higher costs.
Up to now, in order to fill the head with the ink, the following method has been employed. That is, a cap formed of rubber is brought in press contact with a nozzle plate of the head to seal an inside portion between the nozzle plate and the cap. Another tube is attached to an exhaust port provided to the cap which communicates with an external portion. Due to suction by a pump via the another tube, a negative pressure is generated inside a space between the cap and the nozzle plate. As a result, the head is filled with the ink via the tube from an ink cartridge. In this type of ink supplying method, the ink is sucked by only suction from the head side. Thus, if the longer tube is used, the head cannot be smoothly filled with the ink due to the generated flow path resistance.
In view of this, there has been proposed an additional method of filling the head with the ink such that the ink is forced to be pushed out from the ink cartridge side by another pump different from the above pump. However, if being pressurized from the ink cartridge side by using this method, the pressure increases inside the air damper attached to the head which relaxes the inertia of the ink inside the tube, so that the film bonded to the air damper by thermal welding or the like is ruptured due to the internal pressure in some cases.